The term "liquid crystal compound" herein include also compound which do not exhibit a liquid crystal phase by themselves but are useful as a component of liquid crystal compositions.
The term "phase transition temperature" means a temperature range of a nematic phase about the liquid crystal compound, and the term "liquid crystal temperature range" means a temperature range of a nematic phase about the liquid crystal composition.
Display means made of nematic liquid crystals have been used practically in the fields of wrist-watches and desk computers. There has been proposed an idea of using a display means for the display of gauge panelboards of automobiles. As well known, such panelboards should be resistant to a broad range of temperatures ranging from those of cold districts to those of the tropics. It is now required to obtain a liquid crystal composition which works at a broad liquid crystal temperature range of from -30.degree. C. to 80.degree. C.
Liquid crystal composition practically used comprise generally mixtures of several liquid crystal compounds. These liquid crystal compositions exhibit characteristic properties of the respective liquid crystal compounds and they exhibit satisfactory properties required.
As one of the liquid crystal compound, the following compound has been known. ##STR2## This compound is used for elevating the upper limit in the liquid crystal temperature range (i.e. a temperature at which the transition from the nematic phase to isotropic liquid occurs) so as to broaden the liquid crystal temperature range of a liquid crystal composition. However, as the amount of the polycyclic liquid crystal compound is increased, the viscosity and the lower limit of the liquid crystal temperature range (temperature at which the crystalline phase is converted into a nematic phase) are elevated significantly and undesirably.